The present invention relates to a filtering apparatus in which the filter bed can be formed uniformly over the screen plate and thereby a uniform filtration can be effected.
In a filter provided with a screen plate as a filter medium it is usual to collect the filtrate through a supporting member which supports part of the screen plate. In this case, however, if the filtering surface is uniform, the filterate which has passed through an area of the filtering surface in the neighborhood of the collector such as the screen plate supporting member would have been encountered by a smaller internal resistance than that passed through the areas far off the collector. This means that the amount of filtration load is greater at area nearer to the collector than those distant therefrom.
In order to achieve an effective filtration, it is desirable to give a uniform filtering ability over the whole filtering surface. For this purpose, it is to provide a uniform filter bed.
During the precoating a filter aid onto the filter medium by circulating it, there is tendency towards nonuniform formation of the filter bed, because the amount of the precoat liquor containing the filter acid passing through per unit of time is greater in the neighborhood of the collector than that far therefrom, resulting in a greater amount of filter aid being precoated there.
Generally, in prior art filters with a screen plate, the screen plate is supported at the central portion and the filtrate passing through said screen plate is collected using the supporting member. With this construction, however, the unequality between the filtration at the inner portion and that at the outer side portion of the screen plate as mentioned above will be significant, since the collector is only singly provided and, in addition, the collector portion is located far apart from the surrounding large area for the filtration.